The present invention relates to a test device and method for the colorimetric determination of a chemical or biochemical component (analyte) in an aqueous body fluid, such as whole blood. In particular the present invention relates to a dry reagent test strip from which an analyte presence and/or concentration is determined by visual interpretation or through the use of an instrument. A common use of such test strips is for determination of glucose level in blood by diabetics.
Numerous devices have been developed to test for presence and quantity of analytes in aqueous samples, such as whole blood or urine. The patent and technical literature of the last thirty years is replete with inventions which utilize a reagent strip containing a dry chemistry reagent system, that is, a system in which the wet chemistries are imbibed into an absorbent or bibulous medium, dried, and later reconstituted by fluid from the test sample. The reagent strips contain an indicator which changes color, depending on the presence or concentration of a particular analyte in a biological fluid applied to the strip. These strips may be read visually by reference to a color standard or colorimetrically by instrument calibrated or programmed to detect a certain color. Although some of these strips use reduction chemistries, more commonly they involve an oxidizable dye or dye couple. Some of the strips include an enzyme, such as glucose oxidase, which is capable of oxidizing glucose to gluconic acid and hydrogen peroxide. They also contain an oxidizable dye and a substance having peroxidative activity, which is capable of selectively catalyzing oxidation of the oxidizable dye in the presence of hydrogen peroxide. (See, for example, U.S. Pat. No. 5,306,623, to Kiser et al.) Examples of these devices, in addition to those used to test blood glucose, include tests for cholesterol, triglycerides, calcium or albumin in whole blood, and for protein, ketones, albumin or glucose in urine.
Dry chemistry reagent strips incorporating enzyme-based compositions are used daily by millions of diabetics to determine blood glucose concentrations. The NIH sponsored study, the Diabetes Complications and Control Trial, demonstrated conclusively that careful control of blood glucose levels can significantly reduce the incidence of serious complications of diabetes such as vision loss and kidney malfunction. Most diabetics must test themselves periodically in order to make appropriate adjustments to their diet or medication. It is thus especially important for diabetics to have rapid, inexpensive, and accurate reagent strips for glucose determination. The embodiment of dry chemistry reagent systems in test strips enable simple yet effective analytical protocols.
The technologies embodied in the products which have been developed to date have certain limitations from the perspective of the end user and/or the manufacturer. There is, therefore, a need to overcome some of the limitations of currently available colormetric testing systems.
U.S. Pat. No. 3,092,465, issued to Adams et al., U.S. Pat. No. 3,298,789, issued to Mast and U.S. Pat. No. 3,630,957, issued to Rey et al., all describe a basic reagent system which became a standard for colorimetric determination of glucose in biological samples. These patents describe the formation of a film layer or semi-permeable coating over the bibulous matrix to hold back the larger particulates, such as red blood cells, and allow fluid to permeate into the bibulous matrix. This approach requires the removal of red blood cells by washing or wiping to enable visual inspection or instrument reading of the indication of the dye color formed in the matrix.
Stone, U.S. Pat. No. 3,607,093, discloses a membrane for testing blood where the membrane has a skin permeable to solutions but impermeable to solids such as red blood cells and to macromolecules such as proteins. This membrane is disclosed as being used by applying a blood sample then wiping away the red blood cells from the skin in order to reach the test indication through the skin.
U.S. Pat. No. 3,552,928, issued to Fetter discloses the use of certain water soluble salts and amino acids in reagent formulations as separation agents to provide blood separation. With solids such as red blood cells substantially removed from the biological fluid, there is less background color at the test site to obscure a change in coloration produced by a testing reagent.
Phillips et al., U.S. Pat. No. 4,935,346 discloses a system wherein a whole blood sample is applied to the device and indicator development occurs in the presence of the colored components of the sample. Measurements of the color change in indicator are made at two distinct wavelengths to eliminate the interferences from the presence of colored blood components.
Kiser et al., in U.S. Pat. Nos. 5,306,623 and 5,418,142, disclose a visual meter device which incorporates various coatings on a matrix material to filter red blood cells from fluids. Similar devices for visual indication are disclosed by Hochstrasser in U.S. Pat. Nos. 3,964,871 and 4,059,407.
Terminello et al., U.S. Pat. No. 4,774,192, disclose a system in which the matrix is formed of an asymmetric material used to filter the red blood cells in the sample. The asymmetric material has a density gradient from one side to the other to progressively separate red blood cells from the fluids.
Daffern et al., U.S. Pat. No. 4,994,238, disclose a test device that comprises an asymmetric reagent layer that has progressively finer filtration with increased distance from one surface toward the other surface.
Castino et al., U.S. Pat. No. 5,456,835 disclose the use of filters formed of ligand modified polymeric film such as polypropylene fibers and polyethersulfone fibers.
Vogel et. al., U.S. Pat. No. 4,477,575, disclose the use of glass fiber material to achieve blood separation through the thickness of the material. Blood is applied to one side of the glass fiber, and relatively clear fluid migrates out of the opposite side. This fluid is delivered to an additional layer where the detection of analytes can occur.
Macho et al., U.S. Pat. No. 5,451,350, disclose the use of absorbent channels to distribute sample fluid in multi-zone test devices. Charlton et al., U.S. Pat. No. 5,208,163, also disclose the use of capillary channels to distribute blood to various chambers in the device.
The disclosures of the above patents are incorporated herein by reference.
The prior art devices and methods of the above references provide varying degrees of effectiveness of blood analysis at varying degrees of complexity and cost.
It is an object of the present invention to provide improved devices and methods to improve the performance and minimize the cost and complexity compared to the prior art devices.
It is a further object of the present invention to provide a fully disposable, discrete reading system for detecting analyte presence or concentration.
It is another object of this invention to provide a dry reagent chemistry system capable of analyzing whole blood for one or more analytes without prior separation of the red blood cells from the serum.
It is another object of this invention to provide a means for performing microtitration for the analysis of whole blood in a system which enables the ready visual determination of analyte presence or concentration.
It is yet another object of this invention to provide a blood separation system which can be used with a dry chemistry reagent to analyze whole blood for one or more analytes.
It is still a further object of this invention to provide a dry chemistry reagent and test strip which can be used in an electronic meter to analyze whole blood for one or more analytes.
The above objects as well as others are achieved by the devices, methods and systems of this invention as disclosed herein.
In one aspect this invention provides a method of testing blood for the presence or concentration of an analyte by using a porous matrix comprising a skin side and a test side, wherein the skin side comprises a porous skin capable of blocking the passage of red blood cells and of allowing passage of blood fluids containing an analyte to the test side of the matrix, and wherein the test side of the matrix is isotropic for uniform distribution therein of fluid received from the skin side and comprises an indicator capable of indicating the presence or concentration of the analyte. The method comprises applying a blood sample to the skin side of the matrix, allowing the fluid to pass through the skin into the isotropic matrix, then reading or measuring on the test side of the matrix the indication provided by the indicator of the presence or concentration of the analyte without removal of the red blood cells from the skin side of the matrix. The skin side is optionally treated with compounds which assist in blocking the passage of red blood cells and allowing passage of substantially clear fluid. Such compounds, or separating agents, can help facilitate the wicking of the clear fluid into the test side of the matrix. However, it is preferred that the skin side of the matrix is inherently hydrophilic which facilitates the passage of fluid through the skin to the test side of the matrix while blocking passage of the red blood cells. This separation of the blood on the skin side and reading or measuring the resultant indication on the test side of the matrix makes the determination of the presence and/or concentration of analyte simpler due to the relative absence of red blood cells at the test site of system and due to the absence of the necessity of removing the red blood cells before taking the desired reading or measurement.
In another aspect this invention provides a device for testing blood for the presence or concentration of an analyte comprising a holder comprising an opening for receiving a blood sample; and a porous matrix comprising a skin side and a test side wherein the skin side of the membrane is capable of blocking the passage of red blood cells and of allowing the passage of blood fluids containing an analyte to the test side of the matrix and wherein the test side of the matrix is isotropic for uniform distribution of fluid received from the skin side. The test side of the matrix comprises an indicator for indicating the presence or concentration of an analyte in the fluid. The matrix is attached to the holder so that the skin side is oriented toward the opening in the holder for receiving the blood sample such that when a blood sample is applied in said opening the blood contacts the skin side of the matrix allowing the blood fluids to pass to the test side of the matrix and red blood cells to be retained on the skin side of the matrix. The device can optionally have a support member applied to the test side of the matrix, where the support member has a visual opening through which the indicator is read or measured.
Alternatively, the support member can be a solid layer, and the holder can have a second opening through which the indicator can be read or measured after the fluid passes through the skin and into the matrix extending under the second opening in the holder. In this alternative, the skin side and the test side can be on the same side of the matrix member, but the skin providing the blockage of red blood cells is in a different area from the test area of the matrix. In such an alternative, an adequate seal is provided to prevent whole blood from flowing from the skin area to the test area but only allow blood fluids to pass through the skin to the test side or area of the matrix.
In another aspect this invention provides a method of making a device for testing blood for the presence of an analyte comprising providing a holder comprising an opening for receiving a blood sample and laminating to the holder a porous matrix comprising a skin side and a test side wherein the skin side of the membrane is capable of blocking passage of red blood cells and of allowing passage of blood fluids containing an analyte to the test side of the matrix and wherein the test side of the matrix is isotropic for uniform distribution of fluid received from the skin side. In this embodiment, the skin side of the matrix is in contact with the holder and the opening in the holder communicates with the skin on the skin side of the matrix.
In another aspect this invention provides a device for testing concentration of an analyte in a fluid sample comprising a first member comprising an opening having a predetermined volumetric size and a porous matrix member positioned within said opening in the first member for receiving an amount of fluid to fill the volumetric opening. The matrix member comprises an indicator capable of indicating the presence of the analyte, and the matrix member comprises a skin side and a test side wherein the skin side is capable of blocking the passage of solids present in the fluid and of allowing passage of fluid containing an analyte to the test side of the matrix positioned in the volumetric opening. It is preferred that the skin side of the matrix member is a material which is inherently hydrophilic and facilitates the passage of the fluid through the skin side to the test side of the member. The device can optionally have a support member with a visual opening at least in part aligned with the opening in the first member whereby the fluid sample can be applied to one opening, the skin can block passage of solids but allow passage of fluid to the test side of the matrix and the analyte can be detected in the test side of the matrix through the other opening. Sequentially or simultaneously the predetermined volumetric size of the opening in the first member provides for a quantitative measurement of the concentration of the analyte in the fluid by enabling titration of a known amount of indicator reagent and a given volumetric quantity of fluid containing the analyte and the color indicator provides a qualitative indication. This invention further comprises methods of using these devices to quantitively measure an analyte in a fluid.
In another aspect this invention provides a method of making a device for testing concentration of an analyte in a fluid comprising providing a first member being substantially noncompressible and having an opening therein of a predetermined volumetric size and providing a porous matrix member which is fluid permeable and is compressible compared to the first member. The method comprises pressing the matrix member against the first member so that a portion of the matrix member protrudes within said opening and a portion of the matrix member is compressed against the surface of the first member adjacent to said opening. Optionally, a support member with an opening aligned with the opening in the first member can be laminated to the first member to position the compressed portion of the matrix between the first member and the support member. Also, optionally the compressed portion of the matrix member can be removed leaving the portion of the matrix member within the opening. The matrix member used in this method of making such devices optionally can have a skin side wherein such a matrix member is positioned in the devices as described above wherein the skin side protrudes into said opening or the skin side faces the support member.
In another aspect this invention provides a device for the testing for the presence or concentration of an analyte in a fluid sample comprising a first member comprising an opening for receiving a fluid sample, a porous matrix member positioned in communication with and extending laterally from said opening in the first member, where the matrix member comprises an initial area, which is in communication with the opening in the first member, and a test area, which is a given distance laterally from the initial area. The matrix member contains pores which are capable of blocking in the lateral distance between the initial area and the test area the passage of solids in the fluid sample and capable of allowing passage of fluid the lateral distance from the initial area to the test area of the matrix. The test area of the matrix comprises an indicator capable of indicating the presence or concentration of the analyte. This device can optionally comprise a support member comprising an opening therein on which the first member and the matrix member are mounted so that the matrix member is positioned between the first member and the support member and so that the opening in the support member is offset from the opening in the first member and is positioned over at least a portion of the test area of the matrix. This device is capable of receiving a fluid through one opening at the initial area of the matrix, allowing the fluid to pass laterally though the matrix from the initial area of the matrix to the test area of the matrix while the pores of the matrix provide blocking of the passage of solids. The other opening at the test area of the matrix is a visual opening which allows detection of the indication of the indicator. Alternatively, the second opening at the test area of the matrix member can be in the first member at the given lateral distance from the opening at the initial area of the matrix. The optional support member may be solid with no openings. In this alternative device, the fluid sample is received in the first opening at the initial area and the indicator read at the second opening at the test area where both openings are on the same side of the device.
In the above embodiments utilizing lateral flow of the fluid, an anisotropic or asymmetric porous matrix can be used. For example, in such a matrix separation of solid components can occur based on decreasing or changing pore size in the matrix. However, in such embodiments an isotropic porous matrix may be employed where uniform sized pores block the passage of solids. In either case, the solids such as red blood cells, introduced at the initial area of the matrix can be held back from the test area of the matrix. If the solids are not adequately blocked and are allowed close to the test area, the solids may cast a shadow or cause color difference in the test area of the matrix. In such cases compensation may need to be made in the reading of the indicator.
In another aspect this invention provides a device for testing for the presence or concentration of an analyte in a fluid sample comprising a member having a first opening for receiving a fluid sample and a second opening for receiving fluid from the first opening wherein the first opening and the second opening are connected by a restricted flow passageway or delivery channel communicating with the first opening and second opening thus enabling the fluid sample to flow from the first opening to the second opening through the restricted flow passageway. This device further comprises a detector for detecting and measuring the rate of initial flow of the fluid from the first opening through the restricted flow passageway towards the second opening. This aspect of the invention also provides a method of using such device wherein the rate of initial flow of fluid through the restricted passageway is measured and correlated to the concentration of a particular concentration of solids (e.g., hematocrit level) in the fluid sample. It has been found that the rate of initial flow of fluid through the restricted flow passageway can be directly correlated to the concentration of an analyte and the fluid. Optionally, in this aspect of the invention the second opening may contain a porous matrix positioned in the second opening comprising an indicator for indicating the presence or concentration of an analyte in the fluid sample entering the matrix. Also, optionally, the porous matrix positioned in the second opening may comprise a skin side and a test side as described above in connection with other embodiments of this invention. In this aspect of the invention the measurement of the rate of initial flow of the fluid through the restricted flow passageway can also be correlated to the indication provided by the indicator in the matrix in the second opening thus providing more complete information with respect to the hematocrit level of the fluid. Also optionally a matrix material may be present in the restricted flow passageway or delivery channel, and the initial flow rate therethrough can be correlated to an hematocrit level of the blood as described above.
The above embodiments of the devices of the invention with the appropriate dry chemistry system in the matrix member can be used in test strips which may be read visually or measured in an electronic meter. Electronically read devices or strips are provided with appropriate calibration data and test initiation sequences which can be incorporated on the strips in the form of bar codes, digital punches, magnetic signals or the like. These codes or signals on the test strips provide appropriate data to the meter and eliminate the need for inputs from the user. These aspects simplify the test protocol and reduce the potential for user generated error.
The above sets forth the generic aspects of the various devices and methods of the present invention. These devices and methods are more fully described in the drawings and the descriptions below.